Wear-resistant, corrosion-resistant cobalt base alloy

ABSTRACT

This invention relates to a novel cobalt-base alloy having good wear resistance and good corrosion resistance characteristics, which consists of 5.00 - 10.00 percent by weight of Cr, 2.50 4.00 percent by weight of B, 0.20 - 2.00 percent by weight of Mn, 0.20 - 2.00 percent by weight of Si, up to 1.00 percent of Fe and up to 2.00 percent by weight of Ni, the balance being Co. When this alloy is used as a lining material for a machine part, such as a steel cylinder or the like, the life of the machine part combined with the alloy can be greatly prolonged.

l States Patent [1 1 Yokota et al.

[45] Jan, 2 1974 WEAR-RESISTANT,

CORROSION-RESISTANT COBALT BASE ALLOY [75] Inventors: Minoru Yokota; Morimichi Tanaka,

both of Fukuoka, Japan [73] Assignee: Hitachi Metals, Ltd., Tokyo, Japan [22] Filed: Nov. 24, 1972 [21] Appl. No.: 309,002

[30] Foreign Application Priority Data Nov. 26, 197i Japan 46-94456 [52] US. Cl. 75/171, l48/32.5 [51] Int. Cl. ..L C226 19/00 [58] Field of Search 75/171, 170; 148/32, 32.5

[56] References Cited UNITED STATES PATENTS 2,864,693 12/1958 Cape et al 75/171 Primary ExaminerRichard 0. Dean Attorney, Agent, or Firm-Raymond C. Stewart 57] ABSTRACT machine part, such as a steel cylinder or the like, thelife of the machine part combined with the alloy can be greatly prolonged.

3 Claims, No Drawings WEAR-RESISTANT, CORROSION-RESISTANT COBALT BASE ALLOY FIELD OF THE INVENTION This invention relates to a cobalt base alloy and, in particular, the invention relates to a cobalt basealloy having a high wear-resistance and a high corrosionresistance in combination.

BACKGROUND OF THE INVENTION Cylinders of plastic molders, mortar pumps, compressors and the like always make a sliding-movement while being in contact with a corrosive or wearing material. For instance, the cylinder of a plastic molderalways makes a sliding movement while in contact with a resin or with additives incorporated therein during the molding operation. Accordingly, in order to prevent wear and corrosion in the cylinder as much as possible, it is desirable to providea lining of an alloy having both a wear-resistance and a corrosion-resistance property on the inner surface of the steel cylinder.

A known wear-resistant alloy having a cobalt-nickel LII base consisting of 40 45 percent of Ni, 40 45 percent of Co., 6 8 percent of Cr and 3- 4 percent of B (hereinafter referred to as alloy A) is defective in that it lacks the necessary corrosion resistance, and a known anti-corrosive iron base alloy of high hardness consisting of 0.2 2.5 percent of B, the balance being iron (hereinafter referred to as alloy B), is insufficient with respect to wear-resistance. Therefore, it is difficult to prolong the life of a steel cylinder or the like by using such known alloys as the lining on the surface of the cylinder or the like.

It is therefore a primary object of this invention to provide a cobalt base alloy having a good combination of a high wear-resistance and a high corrosionresistance.

Another object of this invention is to provide a cobalt base alloy having improved wear-resistance and corrosion-resistance which can prolong the life of a part of a machine which slides or moves while in contact with a'wearing and corrosive material and which also can prolong the life of the machine per se, when said alloy is used as a lining for such a machine part.

These and other objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following specification and claims.

SUMMARY OF THE INVENTION The wear-resistant and corrosion-resistant cobalt base alloy of this invention consists of 5.00 10.00 percent by weight of chromium, 2.50 4.00 percent by weight of boron, 0.20 2.00 percent by weight of manganese, 0.20 2.00 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt. It is preferred that the alloy of this invention have a composition of 5.00 10.00 percent by weight of chromium, 2.50- 4.00 percent by weight of boron, 0.70 1.30 percent by weight of manganese, 0.70 1.30 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt. An alloy most suitable for attaining the objects of this invention can be provided when the alloy is formed with a composition consisting of 6.02 8.00 percent by weight of chromium, 2.65-3.61 percent by weight of boron, 0.95 1.12 percent by weight of manganese, 1.08 1.15 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt.

DETAILED DESCRIPTION OF THE INVENTION 1 As noted above, the alloy of this invention has a composition consisting of 5.00 10.00 percent by weight of chromium, 2.50 4.00 percent by weight of manganese, 0.20 2.00 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt. Such an alloy has a structure composed of a cobalt-chromium boride having a Vickers hardness Hv of 1,000 to 1,300 and a cobalt-chromium solid solution having a Vickers hardness Hv of 300 to 400. The average hardness of the alloy of this invention is to 80, expressed in the terms of Shore hardness Hs. Since the contents of nickel and iron are very small, the alloy of this invention has a hardness higher than the hardness Hs of 64 70 of the above alloy A, which has been known asa wear-resistant alloy, and yet, in addition, the alloy of this invention has an excellent wear-resistance.

In the alloy of this invention, the contents of iron and nickel are limited to up to 1.00 percent by weight and up to 2.00 percent by weight, respectively. When the contents of nickel and iron are increased in excess of said upper limits, the hardness of the aboye-mentioned cobalt-chromium solid solution is reduced, which in turn results in a reduction of the hardness of the entire alloy. In the above alloy A, the hardness Hv of the solid solution is within the range of from 200 to 250, and the hardness Hs of the alloy per se is within the range of from 64 to 70. In an iron-nickelcobalt-base alloy formed by incorporating 10 15 percent by weight of iron into said alloy A, the hardness Hv of the solid solution is within the range of from 170 to 220, and the hardness Hs of the entire alloy is within the range of from 61 to 68. As described above, when a part of the cobalt content is replaced by nickel and/or iron in the alloy of this invention, a reduction of the hardness of the entire alloy is brought about owing to the reduction of the hardness in the solid solution, and it is therefore impossible to obtain an alloy excellent in hardness characteristics.

Further, since the iron content is up to 1.00 percent by weight, the alloy of this invention is very excellent with regard to its corrosion resistance over the above alloy B, which is known as an anti-corrosive iron base alloy, even though the alloy of this invention is somewhat inferior to alloy B in respect to its hardness characteristics. More specifically, when the alloy is compared with alloy B with respect to the ratio of corrosion by an aqueous solution of hydrochloric acid or sulfuric acid (50 percent), it is apparent that the corrosion ratio in the alloy of this invention is 1/10-1/30 of that in allby B and, hence, it can readily be seen that the corrosion ratio of the alloy of this invention is very small. Further, the ratio of corrosion of the alloy of this invention by a chlorine gas atmosphere is l/ 1/500 of that of said known alloys. Thus, it W1II readily be understood that the alloy of this invention has a very excellent corrosion-resistance.

The chromium is present in a dissolved state in the cobalt to form a solid solution, and it is effective for increasing the hardness of the solid solution. However, when it is incorporated in an amount less than 5 percent by weight, the hardness of the solid solution is insufficient. On the other hand, at a chromium content exceeding 10 percent by weight, the brittleness of the alloy is increased. Therefore, the chromium is incorporated in the present alloy in a content of 5 to percent by weight.

The boron is precipitated in the alloy structure in the form of a boride having a high hardness. In an alloy containing boron in an amount of less than 2.50 percent by weight, the hardness I-Is is below 70, and at a boron content exceeding 4.00 percent by weight, the brittleness of the alloy is increased with precipitation of free boron and the hardness Hs is so low as not to exceed 70. Therefore, the boron content is adjusted within a range of 2.50 to 4.00 percent by weight.

In this invention, it is essential that manganese and silicon should be incorporated as deoxidents in amounts of 0.20 2.0 percent by weight, preferably 0.70 1.30 percent by weight, respectively. The manganese and silicon increase the deoxidizing effect during the lining treatment or the like and help to prevent the occurrence of defects such as pin holes and blow holes in the lining layer.

As described above, it is indispensable that the iron content should be limited to up to 1 percent by weight so as to impart an excellent corrosion-resistance to the alloy and that the nickel content should be limited to up to 2.00 percent by weight so as to impart an excellent wear-resistance to the alloy.

The cobalt is bound with the chromium and boron to impart high hardness characteristics and high corrosion resistance to the resulting alloy. Thus, cobalt is used as the alloy base and occupies the balance of the composition of the alloy.

In case that the contents of the above constituents of the alloy of this invention are so selected that the alloy has a composition consisting of 6.02 8.00 percent by weight of chromium, 2.65 3.61 percent by weight of boron, 0.95 1.12 percent by weight of manganese, 1.08 1.15 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt, the composition of the resulting alloy is within an eutectic crystal-forming range and the melting point of the alloy is as low as 1,105-1,l 10 C. Therefore, forming of a lining layer from such an alloy is very easily accomplished and the resulting lining is very compact without any substantial occurrence of defects.

In this invention, excellent wear resistance and excellent corrosion-resistance can be obtained for the first time when the composition of the alloy-constituting ingredients is within the above-mentioned specific range. As described above, the alloy of this invention having such a specific composition has an excellent wearresistance characteristic with respect to alloy A, which is known as a wear-resistant and corrosion-resistant a1- loy, and also is very excellent over alloy B, known to be a wear-resistant alloy, with respect to corrosionresistance, even though the alloy of this invention is a little inferior to alloy B with respect to wear-resistance. Therefore, the alloy of this invention is suitable as a lining material for a machine or apparatus in which such properties are required. For instance, when the alloy of this invention is lined on the inner surface ofa steel cylinder, it is possible to manufacture a composite cylinder constructed of a cylinder body of steel and an inner lining of the alloy of this invention, which has in combination an excellent wear-resistance and an excellent corrosion-resistance.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following Examples are given merely as illustrative of the present invention and are not to be considered as limiting. Unless otherwise noted, the percentages therein and throughout the application are by weight.

XAMPLE '1' The starting metals constituting the alloy of this invention were charged into a graphite crucible and were molten at 1,400 1,500 C. in a high frequency induction furnace to obtain a platelike cast product. As a result of analysis, it was confirmed that the composition of the cast alloy product consisted of 7.96 percent by weight of chromium, 3.16 percent by weight of boron, 0.96 percent by weight of manganese, 0.84 percent by weight of silicon, 0.84 percent by weight of iron and 1.40 percent by weight of nickel, the balance being cobalt, and the hardness I-Is of the cast alloy product was 83.

This cast alloy product was ground and charged into a cylinder of chromium-molybdenum steel (SCM-4 according to the Japanese Industrial Standard) having an outer diameter of 130 mm and an inner diameter of mm in an amount necessary for forming a lining layer of a thickness of 2 mm, and both ends of the cylinder were sealed with iron lids, following which the cylinder was allowed to stand still in a furnace maintained at about 1,200 C for 1 hour. The cylinder was taken out from the furnace and immediately constructed into a centrifuge, and a rotation of 1,540 ppm was given to the cylinder. After the cylinder was cooled to 850 C, the rotation was stopped and the cylinder was gradually cooled to room temperature over a period of 48 hours. The iron lids were taken from the cylinder, and the condition of the lining layer was examined. As a result, it was found that the lining layer had a thickness of 2 mm and was fusion-bonded in a uniformly diffused manner to the inner wall of the cylinder and that the hardness I-Is of the lining layer was 80.

EXAMPLE 2 In the same manner as described in Example 1, a plate-like cast product of an alloy of this invention having a composition different from that of the alloy of Example 1 was prepared. Namely, the alloy of this Example had a composition consisting of 8.06 percent by weight of chromium, 3.61 percent by weight of boron, 0.95 percent by weight of boron, 0.95 percent by weight of manganese, 1.15 percent by weight of silicon, 0.90 percent by weight of iron and 0.80 percent by weight of nickel, the balance being cobalt. The hardness Hs of the cast alloy product was 88.

This cast alloy product was ground and packed in a cylinder of carbon steel for machine structural use (S-45C according to the Japanese Industrial Standard) having an outer diameter of mm and an inner diameter of 40 mm in an amount sufficient to form a lining layer of a thickness of 2 mm. Both ends of the cylinder were sealed and the cylinder was maintained for 1 hour in a furnace at about 1,200 C. Then, the cylinder was taken from the furnace and immediately constructed into a centrifuge. A rotation of 1,000 ppm was given to the cylinder. After the cylinder was cooled to 800 C., the rotation was stopped and it was then gradually cooled to room temperature over a period of 25 hours. Then, the condition of the lining layer was examined. As a result, it was found that the lining layer was fixedly fusion-bonded in a uniformly diffused manner in a thickness of 2 mm to the inner wall of the cylinder and that the hardness Hs of the lining layer was 84.

EXAMPLE 3 In the same manner as described in Example 1, a plate-like cast product of an alloy of this invention having the composition consisting of 6.02 percent by weight of chromium, 2.65 percent by weight of boron, 1.12 percent by weight of manganese, 1.08 percent by weight of silicon, 0.85 percent by weight of iron and 0.80 percent by weight of nickel, the balance being cobalt, was prepared. The hardness Hs of this cast alloy product was 80.

This cast alloy product was ground and charged into a cylinder of a carbon steel for machine structural use (S-400C according to the Japanese Industrial Standard) having an outer diameter of 190 mm and an inner diameter of l 13 mm in an amount sufficient to form a lining layer of a thickness of 1.5 mm. Both ends of the cylinder were sealed with iron lids and the cylinder was maintained for 1 hour in a furnace at about 1,200 C. Then, the cylinder was taken from the furnace and immediately constructed into a centrifuge. A rotation of 930 ppm was given to the cylinder and it was cooled to 800 C. Then, the cylinder was gradually cooled to room temperature over a period of 48 hours. As a result of the examination of the condition of the lining layer, it was found that the inner lining of a thickness of 1.5 mm was fixedly fusion-bonded in a uniformly diffused state to the inner wall of the cylinder and that the hardness Hs of the lining layer was 79.

In the same manner as described in Example 1, a cast product of an alloy having the same composition as the above-mentioned known alloy A was prepared. Namely, the composition of the alloy consisted of 8.00 percent by weight of chromium, 3.28 percent by weight of boron, 0.99 percent by weight of manganese, 1.29 percent by weight of silicon, 4 percent by weight of nickel and 41 percent by weight of cobalt. The hardness Hs of this cast alloy product was 68.

This cast alloy product was ground and it was lined on the inner surface of a cylinder in the same manner as described in Example 1 under the same lining conditions as adopted in Example 1. The hardness Hs of the resulting lining layer was 68.

Thus, it can be seen that the hardness Hs of the lining layer of the alloy of this invention was higher by 10 16 than that of thelining layer of said conventional alloy. In each of the lining layers of the alloy of this invention and of the conventional alloy, the hardness I-Iv of the boride was 1,200 on the average, but the average .hardness Hv of the solid solution was 390 in the alloy of this invention, while the average hardness Hv of the solid solution was 256 in the conventional alloy. From the foregoing, it will readily'be understood that the hardness of the solid solution in the alloy of this invention is much higher than that in the conventional alloy and that the hardness of the entire alloy is higher in the alloy of this invention than in the conventional alloy.

The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.

What is claimed is:

l. A wear-resistant, corrosion-resistant cobalt base alloy consisting essentially of 5.00 10.00 percent by weight of chromium, 2.50 4.00 percent by weight of boron, 0.20 2.00 percent by weight of manganese, 0.20 2.00 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt.

2. A wear-resistant, corrosion-resistant cobalt base alloy consisting essentially of 5.00 10.00 percent by weight of chromium, 2.50 4.00 percent by weight of boron, 0.70 1.30 percent by weight of manganese, 0.70 1.30 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt.

3. A wear-resistant, corrosion-resistant cobalt base alloy consisting of 6.02 8.00 percent by weight of chromium, 2.65 3.61 percent by weight of boron, 0.95 1.12 percent by weight of manganese, 1.08

1.15 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight 0 nickel, the balance being cobalt. 

2. A wear-resistant, corrosion-resistant cobalt base alloy consisting essentially of 5.00 - 10.00 percent by weight of chromium, 2.50 - 4.00 percent by weight of boron, 0.70 - 1.30 percent by weight of manganese, 0.70 - 1.30 percent by weight of silicon, up to 1.00 Percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt.
 3. A wear-resistant, corrosion-resistant cobalt base alloy consisting of 6.02 - 8.00 percent by weight of chromium, 2.65 -3.61 percent by weight of boron, 0.95 - 1.12 percent by weight of manganese, 1.08 - 1.15 percent by weight of silicon, up to 1.00 percent by weight of iron and up to 2.00 percent by weight of nickel, the balance being cobalt. 